Cannot create an array of SinkInputInfo

Question

I cannot make an array of SinkInputInfo objects. I've posted this to the appropriate repo but got no response.

Minimal reproduction:

using PulseAudio;

public void main () {
    SinkInputInfo[] sink_inputs;
}

Outputs

/tmp/test.vala.PFQW80.c: In function ‘_vala_pa_sink_input_info_array_free’:
/tmp/test.vala.PFQW80.c:18:4: warning: implicit declaration of function ‘pulse_audio_sink_input_info_destroy’ [-Wimplicit-function-declaration]
   18 |    pulse_audio_sink_input_info_destroy (&array[i]);
      |    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/bin/ld: /tmp/ccZQGm6J.o: in function `_vala_pa_sink_input_info_array_free':
test.vala.PFQW80.c:(.text+0x3f): undefined reference to `pulse_audio_sink_input_info_destroy'
collect2: error: ld returned 1 exit status
error: cc exited with status 256

have you tried instantiating it as an object without being an array ? — midugh, Sep 02 '21 at 18:53
I need to store an array of them, not just one. I'm not really sure what you mean, sorry. I have no issues storing a single SinkInputInfo object in a var — ChildishGiant, Sep 02 '21 at 18:58
That was my question. Now we know the error does not com from the object itself, I guess you are missing a header somewhere. What the error says basically is that when the destroyer will be called (namely `pulse_audio_sink_input_info_array_free`) it will result into an error as the function is undefined — midugh, Sep 02 '21 at 19:00
So something's wrong with my vapis? Are you able to replicate this issue? — ChildishGiant, Sep 02 '21 at 19:21
Hmm, I was previously able to create a single object but now that gives me a similar issue. — ChildishGiant, Sep 02 '21 at 19:40
I wasn't able to re-create the issue, but have you tried downloading again the `c` or `vala` *dev* libraries ? sometimes, you do not have all the dev libs which makes the linking fail — midugh, Sep 02 '21 at 20:36
I was able reproduce this without an issue on another install. I've got `libpulse-dev` installed and can use other parts of the library. I've completely ran out of things to debug really. I've reinstalled all the libs, tools etc and still have the issue so have no clue. — ChildishGiant, Sep 02 '21 at 21:14
I haven't got any experience with `vala`, but can you access the compiler options (you could retrieve them on your other install ). If so check the linker has the `-lpulse` flag specifying linking to pluse audio library — midugh, Sep 02 '21 at 21:17

score 2 · Accepted Answer · answered Sep 03 '21 at 11:02

You can not create an instance of SinkInputInfo. You can also not store instances of it anywhere.

The reason is that it is intended to be only valid inside the callbacks:

https://www.freedesktop.org/software/pulseaudio/doxygen/introspect.html#query_sec

Data members in the information structures are only valid during the duration of the callback. If they are required after the callback is finished, a deep copy of the information structure must be performed.

libpulse does not provide any means to copy or free the SinkInputInfo pointer type.

You can however use anything inside the struct:

Gee.ArrayList<string> sink_inputs;

public void cb(PulseAudio.Context c, PulseAudio.SinkInputInfo? i, int eol) {
        sink_inputs.add(i.name);
}

public void main () {
    var loop = new PulseAudio.MainLoop();
    var context = new PulseAudio.Context(loop.get_api(), null);
    sink_inputs = new Gee.ArrayList<string>();
    context.get_sink_input_info_list(cb);
}

Here I only store the name property. You could extend this by creating your own data type in vala and copying over anything you are interested in.

Also the vapi file is incomplete, there are ways to tell the Vala compiler that copying and memory management is not available. See https://wiki.gnome.org/Projects/Vala/ManualBindings#Structs

I haven't done any Vala code in a while, but I think the vapi file should set the destroy_function to an empty string.

In summary: Do not try to store the SinkInputInfo argument of the callback anywhere, just copy the fields of the struct you are interested in.

Cannot create an array of SinkInputInfo

Minimal reproduction:

Outputs

1 Answers1